1. Field of the Invention
The present invention relates to a novel phosphorus compound having a phosphate-phosphonate bond in one molecule. As used herein, the term “phosphate-phosphonate bond” refers to a bond between a phosphorus atom and another phosphorus atom which is provided by a linking group formed of an alkylene, which may have one or more substituents, and an oxygen atom. In this specification, a compound having a phosphate-phosphonate bond in one molecule is referred to as a “phosphate-phosphonate compound” for the sake of simplicity.
Such a compound is useful as a flame retardant agent, especially, as a flame retardant agent for a resin material.
In another aspect of the invention, the present invention relates to a flame retardant polyester fiber which contains, as a flame retardant agent, an organic phosphorus compound having a phosphate-phosphonate bond in one molecule and is superb in flame retarding property, thermal resistance, and hydrolysis resistance. More specifically, the present invention relates to a flame retardant polyester fiber which is flame-retarded by the phosphorus compound and thus is less adversely influenced regarding various properties of the fiber, does not contain halogen, and is durable against washing.
In still another aspect of the invention, the present invention relates to a flame retardant polyurethane resin composition. In more detail, the present invention relates to a flame retardant polyurethane resin composition which contains, as a flame retardant agent, a specific organic phosphorus compound having a phosphate-phosphonate bond in one molecule, and is superb in flame retarding property, thermal resistance, and volatilization resistance.
2. Description of the Related Art
Phosphorus compounds are generally used in various fields as multi-functional compounds, and various types of phosphorus compounds have been developed. Among those functions, phosphorus compounds are conventionally known as being useful as a flame retardant agent. Phosphorus compounds can be used as a flame retardant agent for a wide range of resins, for example, thermoplastic resins including polycarbonate, ABS resins, and PPE; thermosetting resins including polyurethane resins, epoxy resins, and phenol resins; and resins or fibers of polyester including polyethylene terephthalate, and polybutylene terephthalate.
The flame retarding property of a phosphorus compound generally relies on the phosphorus content thereof. When a phosphorus compound is used for a resin in an amount which is sufficient to provide an intended level of flame retarding property, the physical properties of the resin may significantly be lowered. Therefore, a phosphorus compound having a high phosphorus content is desired in order to provide a sufficient level of flame retarding property with a smaller amount of phosphorus compound.
Further, a flame retardant agent for a resin is exposed to a very high temperature for kneading or molding the resin. Accordingly, a phosphorus compound having a high stability at a high temperature is desired.
Among the above-mentioned resin and fiber materials, polyester fibers are used in various fields including clothing, interior products, filing cotton, non-woven cloth, and materials for industrial use, for its superb dynamic characteristics and ease of processing. The polyester fiber products used for interior decoration of hotels, hospitals, movie theaters and the like are strictly restricted by the Fire Services Act, in order to minimize damages of fires caused by matches, cigarettes and the like. As the awareness of disaster prevention of the general public has been increased recently, development of flame retardant polyester fiber products has been desired in order to create a highly safe and comfortable living environment.
The flame retarding property of a phosphorus compound generally relies on the phosphorus content thereof. Namely, in general, as the phosphorus content is higher, the flame retarding property is higher. This general principle is not necessarily true for flame-retarded polyester fibers.
For example, even when a phosphorus compound having a high phosphorus content is used, the flame-retarded polyester fiber may have the phosphorus compound merely adhering to the surface of the fiber, without penetrating deep into the fiber. Clothing or the like, which is produced of the flame-retarded fiber in such a state, is not continuously provided with the intended level of flame retarding property since the phosphorus compound is easily detached from the fiber by washing.
Conversely, even a phosphorus compound having a low phosphorus content can provide an intended level of flame retarding property if the phosphorus compound fully penetrates into the polyester fiber and strongly adheres to the polyester fiber physically.
Accordingly, a phosphorus compound desired in the technical field of polyester fibers has a high phosphorus content such that the amount of phosphorus compound can be reduced to provide a sufficient level of flame retarding property. In addition, a phosphorus compound which is not easily detached from the polyester fiber is desired in the technical field of polyester fiber.
Polyurethane resins are mainly used in various fields of products for daily life, including automobile upholstery, furniture, materials for electrical devices, and building materials, for their characteristics of being low cost, lightweight, and easy to shape. Polyurethane resins are mostly used as polyurethane foams. However, polyurethane resins, which are polymeric organic compounds, are inflammable and may possibly cause an uncontrollable combustion once ignited. A fire caused in a living environment may lead to disaster affecting people's lives. From this point of view, the polyurethane foam production industry has made efforts to avoid fires by introducing flame retardation technology into the foams. Today, parts of the products formed of polyurethane foams, including automobile upholstery, furniture, and materials for electrical devices, are legally required to be flame retardant. Such legal regulations are provided by, for example, the UL Standards for electric products and the FMVSS-302 for automobiles in the United States.
In general, a polyurethane resin can be flame-retarded by adding a flame retardant agent when foaming the polyurethane resin. When a flame-retardant agent is added to the polyurethane resin in an amount which is sufficient to provide an intended level of flame retarding property, the physical properties of the polyurethane resin may be significantly lowered. Accordingly, a phosphorus compound having a high phosphorus content is desired in order to provide a sufficient level of flame retarding property with a smaller amount of phosphorus compound. However, use of a phosphorus compound having a high phosphorus content does not necessarily guarantee a high flame retarding property or various physical properties required of the polyurethane resin composition.
A type of flame retardant agent, which has increasingly been used recently, foams and carbonizes the material to be flame-retarded at the time of combustion to form a char, and thus cuts off oxygen and provides a flame retardation effect. Such a property of the flame retardant agent is referred to as intumescent. The effect is not controlled only by the phosphorus content, but often relies on the molecular structure of the flame retardant agent. When the flame retardant agent fulfills the required conditions regarding the phosphorus content and molecular structure, a polyurethane foam having a higher level of flame retarding property can be provided by the synergistic effect. In foaming polyurethane, as the foaming scale is increased, the temperature of the heat accumulated internally is increased. Thus, a phosphorus compound having a high thermal stability at such a high temperature is desired.
Phosphorus compounds are roughly classified by structure into, for example, phosphate, phosphonate, phosphinate, phosphate, phosphonite, phosphinite, phosphine oxide, and phosphine. There are also phosphorus compounds having a plurality of different types of bonds in one molecule. A phosphate-phosphonate compound is one example thereof. More specifically, known examples of phosphate-phosphonate compounds include phosphate-phosphonate compounds containing a halogen atom such as chlorine, bromine or the like in the molecule, phosphate-phosphonate compounds containing an alcoholic hydroxyl group in the molecule, and phosphate-phosphonate compounds containing a short alkyl group such as, for example, an ethyl group.
These phosphate-phosphonate compounds are described in, for example, the following documents:
Japanese Laid-Open Publication No. 2000-328450 (pages 2 to 6);
Japanese Laid-Open Publication No. 57-137377 (pages 1 to 10);
U.S. Pat. No. 4,697,030 (pages 2 to 9);
Zhurnal Obshchei Kimii (1987), 57(12), 2793-4; and
U.S. Pat. No. 3,060,008 (pages 1 to 3).
For example, Japanese Laid-Open Publication No. 2000-328450 discloses a technology for using a phosphate-phosphonate compound containing a halogen atom to flame-retard a metha-type aromatic polyamide fiber. Japanese Laid-Open Publication No. 57-137377 discloses a technology for using a compound containing a halogen atom such as hexabromocyclododecane to flame-retard a fiber.
However, use of these compounds containing halogen has problems in that when the fiber is, for example, burned, the decomposition of the phosphorus compound used as the flame retardant agent generates gas harmful to the human body such as hydrogen halides or the like, corrodes the incinerator, or generates dioxin, which is more harmful than hydrogen halides.
U.S. Pat. No. 4,697,030 discloses a phosphate-phosphonate compound containing an alcoholic hydroxyl group, and examples of using a phosphate-phosphonate compound for a polyester fiber and a polyurethane foam.
However, a phosphate-phosphonate compound having an alcoholic hydroxyl group is not superb in water resistance. For example, when a phosphate-phosphonate compound having an alcoholic hydroxyl group is added to a polyester fiber, as the product formed of the fiber and the compound is washed repeatedly, the phosphate-phosphonate compound is gradually eluted to the washing water since the compound has affinity with water. As a result, the flame retarding property of the fiber is easily lowered.
This problem is solved by using a method of reacting the above-mentioned phosphorus compound when synthesizing polyester and thus incorporating the phosphorus compound into the backbone structure of the polyester. Such a reaction cannot be performed by processing manufacturers, which use a method of simply purchasing a polyester fiber and allowing a flame retardant agent to be absorbed into the polyester fiber (post-processing method). In other words, there is a limit in the manner of using the phosphorus compound.
A polyurethane foam is generally produced by reacting two types of hydroxyl groups, i.e., hydroxyl groups of polyol and a hydroxyl group of water as a foaming agent, with isocyanate groups of polyisocyanate. When this phosphorus compound is used for a polyurethane foam, there occurs a necessity of controlling the reaction of these three types of hydroxyl groups having different reactivities with the is isocyanate group. Due to the difficulty in controlling the reaction, it is very difficult with the conventional compositions to obtain a foam which sufficiently fulfills various physical properties required of the foam. Even if a foam which is superb in various physical properties is obtained, the range of ratios of materials and a catalyst usable for forming a foam is very narrow, and it is disadvantageously required to perform highly strict control in the actual production process of the foam.
A compound described in U.S. Pat. No. 4,697,030 is inferior in hydrolysis resistance and has a problem in storage stability. For example, for dyeing or flame-retarding a polyester fiber, the compound is used in an emulsified state. Since the emulsification stability of the compound is inferior, it is likely that the color is made uneven and oil spots are generated when the polyester fiber is heated to be processed.
Zhurnal Obshchei Kimii (1987), 57(12), 2793-4, discloses a phosphate-phosphonate compound having four ethoxy groups (C2H5O—) in the molecule.
However, this compound is relatively volatile and has the following disadvantages. When this compound is used for, for example, a polyurethane foam, a fogging phenomenon is likely to occur when the resultant polyurethane foam is exposed to a high temperature. As result, it is likely that the flame retarding property of the resultant polyurethane foam is lowered, or gas harmful to the human body is generated.
Zhurnal Obshchei Khimii (1987), 57(12), 2793-4, does not specifically describe or suggest using a phosphorus compound described therein as a flame retardant agent of a polyurethane resin or a polyester fiber.
U.S. Pat. No. 3,060,008 discloses use of a phosphorus compound for uses other than a flame retardant agent; i.e., a technology of adding a compound represented by the following formula (V) to a fuel of engine.
(In the formula, R is either n-butyl, iso-butyl, or sec-butyl.)
However, U.S. Pat. No. 3,060,008 does not specifically describe or suggest a phosphorus compound having a cyclic structure in which two R's are combined to each other.
U.S. Pat. No. 3,060,008 does not specifically describe or suggest using a phosphorus compound described therein as a flame retardant agent of a polyurethane resin or a polyester fiber.